I enjoyed this one a lot, better than Boojum though not as good as Mongoose. The zombie megafish was a great addition to the mythos, and I liked the nods to other off-kilter bits of the universe, particularly the doppelgangers in the mirrors (presumably a "Through the Looking Glass" nod in this world with Carrollian naming).
One thing did irritate me, though by no means ruining the story. The protagonist has the secret in her history that she keeps mentioning and mentioning but it's a long way into the story before we find out what she actually did. If it was a secret she'd suppressed, it makes sense for me not to learn of it until later, but when she dwells on it then that's the kind of POV withholding that really irritates because it distances me from the character.
The best thing about all of this? If it weren't for the Drabblecast, this episode in the Mongoose universe would not exist. Long live the Drabblecast!